1. Technical Field
The present invention relates to Sn—Cu—Ag alloy nanoparticles, a preparation method thereof and ink or paste using the alloy nanoparticles.
2. Description of the Related Art
Nanoparticles, which are particles having a particle size of nano scale, exhibit a number of special properties such as optical, electronic and magnetic properties that differ significantly from those observed in bulk material due to size-dependent properties such as quantum confinement effect and a very high surface area to volume ratio.
Nanoparticle research is currently an area of intense scientific research in catalytic, electronic and magnetic, optical, and medical fields due to such special properties. Nanoparticles are a bridge between bulk materials and molecular structures and preparation of nanoparticles can be classified into two methods, “top-down approach” and “bottom-up approach”.
The top-down approach involves the breaking down of bulk materials. It may easily control size of nanoparticles but may be difficult to provide nanoparticles having a size of less than 50 nm. Thus, the bottom-up approach, which implies assembling single atoms and molecules into larger nanostructures, has currently more attention and involves generally a colloid liquid phase synthesis when nanoparticles are formed from chemical molecular or atom precursors.
Sn—Pb solder materials, especially a material having a low melting temperature (m.p. 183° C.) and including 63/37 Sn/Pb, have been generally used to join a substrate and electronic elements of circuit boards embedded in electronic devices. However, since wastes can contain Pb(lead) found in Sn—Pb solder materials and cause environmental pollution, development on lead-free solder materials has been significantly growing. The Ag—Cu—Sn family among such Pb-free solders has the most promise as the main replacement of Sn—Pb solder. Most of Ag—Cu—Sn solder materials have composition with 95 wt % or less of Sn. The melting temperature is an important factor as the solder material. When higher content of Sn is used, it may be advantage in the melting temperature but it may deteriorate electrical conductivity, thermal stability, uniformity and the like. Thus, 95 wt % of Sn or less has been used. Based on such information, the invention is to provide a method to increase the content of Sn to lower melting temperature of alloy nanoparticles and at the same time to exhibit electrical conductivity and stability.